First of all ,check the battery to make sure it is fully charged, at least 12.6 with a voltmeter.
Second, take off the battery cables to make sure they are clean, and the ground wire going to the block is clean and tight, also.
Next, you will need a test light, have someone turn the key while you check to see if you are getting juice to the smaller wire at the starter (solenoid wire) If there is voltage, it needs a solenoid or starter.
If there isn't voltage, you will have to chase it down to see where the voltage stops, possibly a neutral safety switch, or the switch hooked to the clutch to prevent accidental starting while in gear!